382 
On the Sesamoids of th e Knee- Joint 
tendon instead of being converted into an extra lateral ligament is continuous with 
its fleshy belly as usual and patella is ossified*." According to Macalisteri" the 
plantaris in Peranieles as in Didelphys is small and arises from the outer condyle. 
Of the Dasyuridae Cunningham has dealt with Thylacinus cynocephalus : he 
states that gastrocnemius ai'ises by two very large and powerful heads : (1) The 
outer head which contains the soleus is much the larger of the two and it arises by 
two parts, (a) by a fleshy process fixed to a large sesamoid bone placed upon the 
posterior aspect of the head of the fibula — clearly our parafibular sesamoid, and 
from a powerful ligament which binds the upper part of this bone to the back of the 
external condyle of the femur, (6) by a tendinous slip attached to the outer aspect 
of the external condyle of the femur. (2) The inner head springs not only from the 
back of the inner condyle but also from the whole breadth of the popliteal surface 
at the same level. Plantaris in Thylacinus arises in common with the outer head of 
gastrocnemius and remains fused with its under surface for a considerable distance. 
We have already noted that in Dasyurus macrourus and D. ursin us the sesamoid 
is parafibular (see our p. 375). MacCormickj has studied the myology of the limbs 
of D. viverrinus. He states that the outer head of gastrocnemius " arises directly 
from the sesamoid bone over the upper end of the fibula, and indirectly by two 
strong ligaments which bind this bone to the femur, one being attached to the 
outer border of the popliteal space, and the other passing over the femur to be 
attached to the upper border of the patella§ and to the outer part of the vastus 
eaiernus tendon." He does not refer to popliteus and plantaris. 
Didelphys is the last marsupial to which we shall refer. It represents the later 
stage of the break-up of the parafibula. Gastrocnemius externus arises from external 
condyle and contains a sesamoid — the lateral fabella. Popliteus follows the course 
of this muscle in higher mammals, arising from a groove in the lateral face of the 
external condyle, and contains a cyaiuella. We found no association between 
popliteus and the gastrocnemial fabella. But the cyamella of the Opossum is 
wedged between the under surface of the lateral condyle and the head of the 
fibula (see our Plate XXXIII, Fig. 85), and when the gastrocnemius is replaced 
the fabella lies on the external condyle immediately above the cyamella. 
According to Parsonsjj, however, the fleshy part of popliteus in the Opossum 
acquires an attachment to the fibula, while the tendon is converted into an extra 
lateral ligament. This did not seem to be the case in our specimen, the tendon 
of popliteus passed to the cyamella, which indeed might be looked upon as a 
parafibula, but unless that sesamoid was fused the tendon could hardly be treated 
It is not ossified in Kangaroos and Wallabies and Opossums, although a small bony element has 
been reported in certain cases. 
t Annals of Natural History, 1870, p. 17. 
J Journal of Anatomy and Plii/sioloyy, Vol. xxi. p. 213, 1887. 
g The reader must remember that the patella is cartilaginous in all Marsupials but Perameles 
although the existence in certain cases of a small ossified kernel has been asserted. The attachment 
the fibular crest to the patella iu the case of Platypus may also be borne in mind here. 
II Journal of Anatomy and Physiology, Vol. xxxiv. p. 313, 1900. 
